There is an X-ray detector as one example of a radiation detector. The X-ray detector is provided with, for example, an array substrate including a plurality of photoelectric conversion parts, and a scintillator provided on the plurality of photoelectric conversion parts and converting an X-ray to fluorescence. The photoelectric conversion part is provided with a photoelectric conversion element converting the fluorescence from the scintillator to a charge, a thin film transistor performing switching of storing and release of the charge, a storing capacitor storing the charge, and the like.
In general, the X-ray detector reads out an image data as follows. First, the detector recognizes X-ray incidence from a signal input externally. Next, the detector reads out the stored charge as the image data by turning on a thin film transistor of the photoelectric conversion part performing reading after the passage of a pre-determined time.
However, in this way, since the start of the operation of the X-ray detector depends on a signal from the outside, there is a problem that a processing time becomes longer due to a time lag or the like.
Here, when the thin film transistor of a semiconductor element is irradiated with the X-ray, a current flows between a drain electrode and a source electrode, even if the thin film transistor is in an off state. The drain electrode of the thin film transistor is electrically connected to a data line.
Thus, a technique is proposed, the thin film transistor is set to the off state, and then based on a difference between a value of the current flowing in the data line when the X-ray is irradiated and a value of the current flowing in the data line when the X-ray is not irradiated, a start time of the X-ray incidence is detected.
However, the value of the current flowing in the data line when the thin film transistor is in the off state becomes extremely small. Furthermore, since a large amount of X-ray irradiation to a human body has an adverse effect on health, the X-ray irradiation to the human body is suppressed to the minimum necessary. Therefore, in the case of the X-ray detector used for medical application, the intensity of the incident X-ray is extremely weak, and the value of the current flowing in the data line becomes further small when the thin film transistor is in the off state.
Therefore, there is a fear that even if the value of the current flowing in the data line is detected when the thin film transistor is in the off state, it is difficult to detect accurately the start time of the X-ray incidence.
Thus, it has been desired to develop a radiation detector capable of detecting accurately the start time of the radiation incidence.